High precision network synchronization in an indoor position location system

ABSTRACT

Methods, systems, and devices for synchronizing a position location network. The methods, systems, and/or devices may provide for designating as a master AP one AP from a network. The master AP may broadcast synchronization signals, which other APs in the network may use to synchronize their respective oscillators and/or clocks. In some cases, the master AP and/or a network server (e.g., a tracking management server) may designate acting master APs. The acting master APs may, for example, broadcast synchronization signals to neighboring APs. The acting master APs and/or the master AP may maintain lists of synchronized APs, which may be transmitted among APs and/or to a network server.

BACKGROUND

In some settings, such as in indoor and enterprise environments, it maybe important to easily locate various types of assets or people, orboth. Examples of such settings include hospitals, retail stores,warehouses, etc. The accuracy and speed with which the location ofassets or people is monitored in an indoor setting may be an importantfactor in determining the usefulness of the tracking system. Inaddition, having a location system that is cost effective, scalable, andthat can provide continuous, accurate, and precise location monitoringis also desirable.

Different systems and devices may be used to locate assets and/or peoplein a particular indoor environment. An ultra-wideband (UWB) network, orsome other radio frequency network deployed throughout at least aportion of the indoor environment, may be configured to perform indoortracking. Systems may employ multiple access points (APs) placed atspecific locations in the indoor environment. A location tracking tagalso may be attached to each mobile asset and/or to each person to betracked. The tag may send waveforms (e.g., beacon signals) that arereceived by the APs for ranging measurements to determine the distancebetween the tag and the APs that receive the waveforms. Once thedistances between the tag and at least three different APs are obtained,triangulation or trilateration may be used to estimate the location ofthe asset or person to which the tag is attached.

A position location network may be calibrated to provide accuratelocation measurements. Calibration may include synchronizing each AP toa master AP within the network. It is desirable to obtain the highestprecision synchronization possible, which may require network widesynchronization, not just local synchronization.

SUMMARY

Described below are methods, systems, and/or devices that provide forhigh precision network wide synchronization in a position locationnetwork. The methods, systems, and/or devices may include tools andtechniques that provide for incrementally synchronizing timers andoscillators located at respective APs to the timers and oscillator of amaster AP within a tracking area of a position location network. Thesynchronization may include a coarse frequency and timing acquisitionand a fine frequency and timing acquisition. These techniques may beutilized over a multi-hop wireless network.

A first, or master, AP with one or more oscillators and timers may beused to synchronize neighboring APs. For example, the master AP maybroadcast a synchronization signal, which may include informationrelated to the oscillator frequency and/or timer time (as referred to astimer count). APs within the vicinity may receive the synchronizationsignal and make estimates and/or corrections to their oscillators and/ortimers. Once the other APs synchronize to the master AP, they may sendan acknowledgment message. In some cases, APs that have synchronized tothe master AP and sent an acknowledgment message may be designated asacting master APs. Acting master APs may operate similarly to master APsand may broadcast a synchronization message to neighboring APs, so thatthe neighboring APs may synchronize to the system. The master AP and/ora tracking management server may keep, or update, a list of APs withinthe network that have been synchronized to the system time broadcastfrom the master AP.

A method of synchronizing a position location network is described. Amaster access point (AP) may be selected from among a plurality of APs.Each of the APs may have a reference oscillator and a timer. A firstsynchronization message may be broadcast from the master AP. A firstacknowledgment message may be received at the master AP from each APthat synchronized to the master AP based on the first synchronizationmessage. One or more APs from which an acknowledgment message isreceived may be designated as an acting master AP.

In one embodiment, each AP may be configured with a narrowbandtransceiver and an ultra-wideband (UWB) transceiver. Broadcasting thefirst synchronization message may include broadcasting a narrowbandsignal. The first synchronization message may include informationrelated to an oscillator frequency and a timer count. An AP thatsynchronized to the master AP may be an AP that estimated a frequencyoffset and a time offset with respect to the master AP. Broadcasting thefirst synchronization message may include broadcasting an ultra-wideband(UWB) signal.

In one configuration, an AP that synchronized to the master AP mayinclude an AP that adjusted an oscillator frequency and a timer countbased on the first synchronization message. A second synchronizationmessage may be broadcast from a designated acting master AP. A secondacknowledgment message may be received at the designated acting masterAP from each AP that synchronized to the designated acting master APbased on the second synchronization message. Broadcasting the secondsynchronization message may include broadcasting at least one of anarrowband signal or a UWB signal. The second synchronization messagemay include information related to an oscillator frequency and a timercount.

In one configuration, one or more lists of neighboring APs synchronizedto the one or more designated acting master APs may be received from theone or more designated acting master APs. Receiving the one or morelists may include receiving, from the one or more designated actingmaster APs at the master AP, one or more lists of neighboring APssynchronized to the one or more designated acting master APs. Receivingthe one or more lists may further include receiving, from the master APat a tracking management server, one or more lists of neighboring APssynchronized to at least one of the master AP and the one or moredesignated acting master APs.

A system of synchronizing a position location network is also described.The system may include means for selecting a master access point (AP)from among a plurality of APs. Each of the APs having a referenceoscillator and a timer. The system may further include means forbroadcasting a first synchronization message from the master AP, meansfor receiving, at the master AP, a first acknowledgment message fromeach AP that synchronized to the master AP based on the firstsynchronization message, and means for designating as acting master APsone or more APs from which an acknowledgment message is received.

An apparatus for synchronizing a position location network is alsodescribed. The apparatus may include a processor and memory inelectronic communication with the processor. Instructions may be storedin the memory. The instructions may be executable by the processor tobroadcast a first synchronization message from the master AP, receive,at the master AP, a first acknowledgment message from each AP thatsynchronized to the master AP based on the first synchronizationmessage, and designate as acting master APs one or more APs from whichan acknowledgment message is received.

A computer-program product for synchronizing a position location networkis also described. The computer-program product may include anon-transitory computer-readable medium storing instructions executableby a processor to broadcast a first synchronization message from themaster AP, receive, at the master AP, a first acknowledgment messagefrom each AP that synchronized to the master AP based on the firstsynchronization message, and designate as acting master APs one or moreAPs from which an acknowledgment message is received.

Further scope of the applicability of the described methods andapparatuses will become apparent from the following detaileddescription, claims, and drawings. The detailed description and specificexamples are given by way of illustration only, since various changesand modifications within the spirit and scope of the description willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIGS. 1A and 1B show an example(s) of a position location network inaccordance with various embodiments;

FIGS. 2A and 2B show block diagrams of an example device(s) that may beemployed in position location networks in accordance with variousembodiments;

FIG. 3 shows a block diagram of an example of a position locationnetwork in accordance with various embodiments;

FIG. 4 shows a block diagram of an example of a position locationnetwork in accordance with various embodiments;

FIG. 5 shows a block diagram of an example of a position locationnetwork in accordance with various embodiments;

FIG. 6 shows an example of a position location network in accordancewith various embodiments;

FIG. 7 shows a call flow diagram that illustrates an example of accesspoint synchronization within a position location network in accordancewith various embodiments; and

FIGS. 8, 9, and 10 are flow diagrams that depict a method or methods ofaccess point synchronization within a position location network inaccordance with various embodiments.

DETAILED DESCRIPTION

Methods, systems, and devices are described that address issuespertaining to synchronizing APs within a network of APs in a positionlocation network (as referred to as location tracking and/or positionlocation systems). The methods, systems, and/or devices may includetools and techniques that provide for incrementally synchronizing timersand oscillators located at respective APs. The synchronization mayinclude a master AP with a wired or wireless connection to a centralserver, or tracking management server. The master AP may have a stableoscillator and stable timer(s).

The master AP may broadcast a synchronization signal, which may includeinformation related to oscillator frequency and/or timer time. APswithin the vicinity may receive these signals and make estimates and/orcorrections to their oscillators and timers. In this way, the systemfrequency and/or time broadcast from the master AP may be relayed toother APs. Once the other APs synchronize to the master AP, they maysend an acknowledgment message.

In some cases, APs that have synchronized to the master AP and sent anacknowledgment message may assume the role of acting master AP. Themaster AP and/or a tracking management server may designate synchronizedAPs as acting master APs. Acting master APs may perform a role similarto the master AP. For example, APs in the vicinity of an acting masterAP may synchronize with the acting master AP and acquire the systeminformation, just as if it were synching with the master AP. As thenumber of acting master APs within the network increases,synchronization rate may also increase. That is, the number of APsexposed to synchronization broadcasts may increase as the number ofacting master APs increases, creating a “synchronization wave” thatpropagates out from the master AP. This process may continue until eachAP within the network is synchronized.

Each acting master AP may transmit to the master AP a list ofsynchronized APs. The master AP may keep track of each synchronized APwithin the network. Additionally or alternatively, the master AP mayforward the list(s) of synchronized APs to the tracking managementserver.

The following description provides examples, and is not limiting of thescope, applicability, or configuration set forth in the claims. Changesmay be made in the function and arrangement of elements discussedwithout departing from the spirit and scope of the disclosure. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, the methods described may beperformed in an order different from that described, and various stepsmay be added, omitted, or combined. Also, features described withrespect to certain embodiments may be combined in other embodiments.

First, FIG. 1A depicts an example of a position location network 100 inaccordance with various embodiments. The system 100 provides locationtracking of assets (e.g., objects) or people, or both, throughout thecoverage area 110 associated with an indoor and/or enterpriseenvironment. In some embodiments, the coverage area 110 represents anarea of coverage inside a building, such as a hospital, a retail store,or a warehouse. Within the coverage area 110, multiple APs 105 may bedeployed at specific locations, as may multiple tags 115 (as referred toas tag units and/or location tracking tags), which may be tracked withinthe coverage area 110. Because of their stationary nature, the exactdistance between any two APs 105 is typically known, or may bedetermined, throughout the operation of the system 100. Any two APs 105may ascertain the distance between themselves through a rangingoperation, which may be a two-way ranging operation. The rangingoperation may be performed via communication links 125.

The arrangement of APs 105 shown in FIG. 1A is intended as anon-limiting example. The APs 105 may be deployed or distributed withinthe coverage area 110 in a manner or pattern different from thatdepicted in FIG. 1A. For example, the APs 105 may be arranged atdifferent distances form one another. In some cases, the coverage area110 may represent a two-dimensional deployment, such as a single floorwithin a building. But in some embodiments, the APs 105 are deployed ina three-dimensional manner by placing some of the APs 105 on differentfloors or levels of a building within the coverage area 110.

Each of the APs 105 may be equipped with a narrowband transceiver or aUWB transceiver, or both. Additionally or alternatively, the APs 105 mayinclude one or more oscillators or timers, or both. The oscillators mayeach produce a repetitive, oscillating electronic signal, which may beadjustable and/or variable. The oscillators may be RF oscillators. Theoscillators may be linear- or relaxation-type. In some embodiments, theoscillators are voltage controlled, temperature compensated crystaloscillators (VCTCXO). The timers may include quartz clock(s), they maybe digital, and/or they may be implemented in software.

The APs 105 may need to undergo a calibration procedure in order toincrease the precision and/or accuracy of the tracking system 100.Calibration may include synchronizing the APs 105 to one another, to anetwork 140, and/or to a tracking management server 150. Additionally oralternatively, calibration may include determining coordinates of eachAP 105.

In some cases, one or more APs 105 are designated or selected as masterAPs or acting master APs that facilitate synchronization. Network-widesynchronization of APs 105 may involve designating or selecting a masterAP 105 with a stable oscillator and stable timer. Each of the other APs105 may synchronize their respective oscillators and timers to themaster AP or to an acting master AP. This synchronization may includecoarse and fine synchronization steps, which, in some embodiments,involves receiving and transmitting both narrowband and UWB signals.

Calibration may also include determining the coordinates of each of theAPs 105 within the coverage area 110. Coordinates of each of the APs 105may be determined incrementally, based on known coordinates of one ofthe APs 105 and known or determined distances between APs 105.

Each of the tag units 115 may be attached to an asset or person beingtracked within the coverage area 110. The tag units 115 may be equippedwith a narrowband transceiver or a UWB transceiver, or both. The tagunits 115 may also have one or more oscillators or timers, or both. Theoscillators may each produce a repetitive, oscillating electronicsignal, which may be adjustable and/or variable. The oscillators may beRF oscillators. The oscillators may be linear- or relaxation-type. Byway of example, the oscillators are VCTCXO. The timers may includequartz clock(s), they may be digital, and/or they may be implemented insoftware.

FIG. 1A depicts an example position location network 100 with six tagunits at locations A, B, C, D, E, and F. Over time, these locations maychange as the assets or people to which the tags 115 are attached moveor are moved within the coverage area 110. The system 100, shown withsix tags 115, is intended as a non-limiting example of a positionlocation network. Those skilled in the art will recognize that thesystem 100 is scalable, and it may be capable of tracking more or fewer0assets or people.

The system 100 includes a tracking management server 150, which also maybe referred to as a tag tracking management server. In some embodiments,the tracking management server 150 is connected to the APs 105 through anetwork 140. The connection may be by way of a radio network associatedwith the APs 105. The tracking management server 150 may receiveinformation from the APs 105 to perform various types of calculations,including: determining one or more sets of receive filters for the APs105; detecting whether a tag 115 is mobile or stationary and adjustingupdate rates accordingly; estimating characteristics of communicationchannels; and/or estimating a location of an asset or person beingtracked within the coverage area 110. The tracking management server 150may also schedule or coordinate various operations associated with theAPs 105, including when to have an AP 105 wirelessly communicate (e.g.,when to transmit UWB and/or narrowband signals) with other APs 105 orwith tags 115. In some embodiments, the tracking management server 150stores information about different APs 105 and subsets of APs 105; andit may use stored information to schedule or coordinate variousoperations between individual APs 105 and/or subsets of APs 105.

The APs 105 may communicate with one another by sending and/or receivingUWB signals and/or narrowband signals. The channels between APs 105,which are associated with communication links 125, are oftencharacterized by noise and signal-degrading impedances. It may thereforebe beneficial to maximize the signal transmit power.

FIG. 1B illustrates transmissions or broadcasts between APs 105 and tags115 via communication links 135. In some embodiments, the tags 115communicate with APs 105 via the communication links 135 using either orboth UWB and narrowband signals. Whether a tag 115 communicatesprimarily with narrowband or UWB may be a function of whether the tag115 is mobile or stationary.

An AP 105 may communicate with other APs 105 using either or both UWBand narrowband signals. During this communication a second AP maysynchronize with a first AP. Upon receipt of an acknowledgment messagefrom the second AP, the first AP may designate the second AP as anacting master AP. Once the second AP is designated as an acting masterAP, the second AP may be used by neighboring APs to synchronize theiroscillator and/or timer(s). The neighboring APs may send anacknowledgment message to the second AP to communicate that they havebeen properly synchronized. The second AP may send a synchronizationlist to the first AP including a list of APs that have beensynchronized. The first AP may keep track of which APs within thenetwork have been synchronized. In some cases, the first AP may transmitthe synchronization list to a tracking management server 150.

Next, turning to FIG. 2A, a block diagram illustrates a device 200configured for synchronizing APs in a position location network inaccordance with various embodiments. The device 200 may be an AP 105-a,which may be an example of an AP 105 of FIG. 1A or FIG. 1B, or both. Insome embodiments, the device 200 is a processor. The device 200 mayinclude a receiver module 205, a synchronization module 210, an actingmaster designation module 215, and/or a transmitter module 220. In somecases, the receiver module 205 and the transmitter module 220 are asingle, or multiple, transceiver module(s). The receiver module 205and/or the transmitter module 220 may include an integrated processor.They may also include an oscillator and/or a timer. In some embodiments,the receiver module 205 and the transmitter module 220 are a part of aUWB transceiver module, a narrowband transceiver module, or both.

The device 200 may include a synchronization module 210. Thesynchronization module 210 may include an oscillator and/or timer(s). Itmay also include an integrated processor. The synchronization module 210may prepare a synchronization message to be transmitted to another APwhich includes information based on an oscillator and/or a timer(s). Thesynchronization module 210 may analyze a received message to determine afrequency offset and/or timer offset, or an adjustment that needs to bemade in order to synchronize an oscillator and/or timer. In some cases,the synchronization module 210 may adjust or change an oscillator and/ortimer(s) in order to synchronize with another AP.

The device may include an acting master designation module 215. Theacting master designation module 215 may include an integratedprocessor. The acting master designation module 215 may include adatabase. In some cases, the acting master designation module 215prepares a communication to let another AP know that it may act as amaster AP. A master AP, or an acting-master AP, may have a synchronizedoscillator and/or timer(s) and may be used for synchronization byneighboring APs.

In some embodiments, the components of the device 200 are, individuallyor collectively, implemented with one or more application-specificintegrated circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more processing units (or cores), on one or moreintegrated circuits. In other embodiments, other types of integratedcircuits are used (e.g., Structured/Platform ASICs, field-programmablegate arrays (FPGAs), and other Semi-Custom integrated circuits (ICs)),which may be programmed in any manner known in the art. The functions ofeach unit also may be wholly or partially implemented with instructionsembodied in a memory, formatted to be executed by one or more general orapplication-specific processors.

By way of illustration, the device 200, through the receiver module 205,the synchronization module 210, the acting master designation module215, and the transmitter module 220, may prepare a signal at thesynchronization module 210 including information regarding an oscillatorand/or timer(s). The transmitter module may then transmit the signal toanother AP. The receiver module 205 may receive an acknowledgmentmessage letting the device 200 know that synchronization with the otherAP has been successful. The acting master designation module 215 mayprepare a signal, to be transmitted by the transmitter module 220,including instructions designating the other AP as an acting master AP.

Next, FIG. 2B shows a block diagram of a device 200-a configured forsynchronizing APs in a position location network in accordance withvarious embodiments. The device 200-a may be an example of the device200 of FIG. 2A; and the device 200-a may perform the same or similarfunctions as described above for device 200. In some embodiments, thedevice 200-a is an AP 105-b, which may include one or more aspects ofthe APs 105 described above with reference to any or all of FIGS. 1A,1B, and 2A. The device 200-a may also be a processor. In some cases, thedevice 200-a includes a receiver module 205-a, which may be an exampleof the receiver module 205 of FIG. 2A; and the receiver module 205-a mayperform the same or similar functions as described above for receivermodule 205. In some cases, the device 200-a includes a transmittermodule 220-a, which may be an example of the transmitter module 220 ofFIG. 2A; and the transmitter module 220-a may perform the same orsimilar functions as described above for transmitter module 220.

In some embodiments, the device 200-a includes a synchronization module210-a, which may be an example of the synchronization module 210 of FIG.2A. The synchronization module 210-a may estimate an offset, such as afrequency offset and/or a time offset. Further, the synchronizationmodule 210-a may adjust an estimated offset. In some cases, thesynchronization module 210-a corrects a frequency of an oscillatorand/or a time (or count) of a timer. In some cases, the synchronizationmodule 210-a reports a frequency and/or time so other devices maysynchronize with the device 200-a

In some embodiments, the device 200-a includes an acting masterdesignation module 215-a, which may be an example of the acting masterdesignation module 210 of FIG. 2A. The acting master designation module210-a may prepare a communication to let another AP know that it may actas a master AP. A master AP, or an acting master AP, may have asynchronized oscillator and/or timer(s) and may be used forsynchronization by neighboring APs. Further, the acting masterdesignation module 210-a may prepare a communication including anacknowledgment message informing another device that the device 200-ahas been successfully and/or unsuccessfully synchronized.

In some cases, the device 200-a includes an acknowledgment module 230.The acknowledgment module 230 may prepare communications includingsynchronization information, such as an indication that synchronizationwas successful. Further the acknowledgment module 230 may analyzecommunications from other devices to determine a device to designate asan acting master.

In some cases, the device 200-a includes a synchronized list module 240.The synchronized list module 240 may include an integrated processor. Inan embodiment the synchronized list module 240 includes a database. Thesynchronized list module 240 may keep a list of devices, such as APs,that have been successfully synchronized. In some cases, thesynchronized list module 240 keeps a list of devices that have not beensuccessfully synchronized. The synchronized list module 240 may collectsynchronization information to be transmitted to a tracking managementserver.

According to some embodiments, the components of the device 200-a are,individually or collectively, implemented with one or more ASICs adaptedto perform some or all of the applicable functions in hardware. In otherembodiments, the functions of device 200-a are performed by one or moreprocessing units (or cores), on one or more integrated circuits. Inother embodiments, other types of integrated circuits are used (e.g.,Structured/Platform ASICs, FPGAs, and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of each unitmay also be implemented, in whole or in part, with instructions embodiedin a memory, formatted to be executed by one or more general orapplication-specific processors.

Turning now to FIG. 3, which depicts a block diagram of a system 300configured for synchronizing APs in a position location network inaccordance with various embodiments. The system 300 may include a APs105-c, 105-d, and 105-e, which may be examples of the APs 105 describedwith reference to one or more of FIGS. 1A, 1B, 2A, and 2B. The AP 105-cmay include a memory module 310, which, in some embodiments, includes asoftware module 315. The AP 105-c may include a processor and schedulermodule 320, an oscillator module 330, antenna(s) module 335, a networkcommunications module 340, timer(s) module 350, a transceiver module360, a synchronization module 210-b, and/or an acting master designationmodule 215-b. In some cases, the timer(s) module 350 and/or theoscillator module 330 operate based on a 32 MHz reference timer and/oroscillator. In some embodiments, the AP 105-c and/or the transceivermodule 360 also includes an UWB module 370 and/or a narrowband module380. Each of the components of the AP 105-c may be in communication witheach other. The network communications module 340 may be incommunication with the network 140-a, which may be an example of thenetwork 140 of FIGS. 1A and 1B.

The memory module 310 may include random access memory (RAM) andread-only memory (ROM). In some embodiments, the memory module 310 alsostores computer-readable, computer executable software (SW) code 315containing instructions configured to, when executed, cause theprocessor and scheduler module 320 to perform various functionsdescribed herein related to synchronizing APs in a position locationnetwork. In other embodiments, the software (SW) code 315 may not bedirectly executable by the processor and scheduler module 320; but itmay be configured to cause a computer, e.g., when compiled and executed,to perform the functions described herein.

The processor and scheduler module 320 may include an intelligenthardware device, such as a central processing unit (CPU). The processorand scheduler module 320 may perform various operations associated withsynchronizing APs in a position location network. The processor andscheduler module 320 may use scheduling information received from, forexample, the tracking management server 150, by way of the network140-a, to determine when it is desirable to synchronize APs 105. Theprocessor and scheduler module 320 may perform various operationsassociated with synchronizing APs in a position location network,including determining when to update a synchronization of APs 105,and/or when to update a synchronization list of APs 105.

The transceiver module 360 may include an ultra wideband (UWB)transceiver 370 and/or a narrowband transceiver 380. Either or both ofthe UWB transceiver 370 and narrowband transceiver 380 may include amodem configured to modulate data (e.g., packets) and provide themodulated data to the antenna(s) module 335 for transmission, and todemodulate data received from the antenna(s) module 335. Someembodiments of the AP 105-c include a single antenna; other embodimentsinclude multiple antennas. As shown in FIG. 3, signals transmitted froma tag 115-a may be transmitted to and/or received by the AP 105-c viathe antenna(s) in or connected to the antenna(s) module 335. The AP105-c may also wirelessly communicate with other APs, such as APs 105-dthrough 105-e. In some embodiments, the AP 105-c may receive signals,including UWB, narrowband, and reference signals from other APs 105; andthe AP 105-c may use the received signals for calibrating and/orsynchronizing components of the AP 105-c; and/or the AP 105-c may usethe received signals for determining a location (e.g., a position) of atag unit 115. In some cases, the AP 105-c may transmit received signalsto the tracking management server 150 via the network communicationsmodule 340 and the network 140-a.

The oscillator module 330 may be connected to the UWB transceiver 370.The UWB transceiver 370 may include an UWB modulator and a radiofrequency (RF) transceiver. In some embodiments, the UWB transceiver 370includes, or is in communication with, a timer, such as the timer(s)module 350. The UWB transceiver 370 may include an integrated processor.The UWB transceiver may work with, or for, the synchronization module210-b to synchronize, for example, APs 105.

The transceiver module 360 may further include the narrowbandtransceiver 380. The narrowband transceiver 380 may include anintegrated processor. It may also include a timer and/or oscillator. Insome cases, it is in communication with the oscillator module 330 and/orthe timer(s) module 350. The narrowband transceiver 380 may be capableof communicating with wireless local area network (WLAN) products thatare based on the IEEE 802.11 family of standards (WiFi). In someembodiments, the narrowband transceiver is a two-way digital radio basedon the IEEE 802.15 family of standards (ZigBee). In another embodiment,the narrowband transceiver is a two-way digital radio based on the IEEE802.15.1 family of standards (Bluetooth).

Next, FIG. 4 shows a block diagram illustrating a system 400 configuredfor synchronizing APs in a position location network, which may includea tag unit 115-b. In some embodiments, the tag unit 115-b includes oneor more aspects of the tag units 115 of any or all of FIGS. 1A, 1B, 2A,2B, and 3. The tag unit 115-b may include a controller and schedulermodule 410, a memory module 420, a UWB transceiver module 450, anarrowband transceiver module 460, and antenna(s) module 440. In someembodiments, the tag unit 115 includes an oscillator module 430 or atimer module 435, or both. The oscillator module 450 and the timermodule 435 may each include several oscillators and timers,respectively.

By way of illustration, the controller and scheduler module 410 includeslogic or code, or both, that enables it to control the operations of thetag unit 115-b. In some cases, the controller and scheduler module 410includes a microcontroller or a state machine to control the UWBtransceiver module 450 and the narrowband transceiver module 460.

The memory module 420 may include random access memory (RAM) orread-only memory (ROM), or both. In some embodiments, the memory module420 stores computer-readable, computer-executable software (SW) code 425containing instructions that are configurable to, when executed, causethe controller and scheduler module 410 to perform various functionsdescribed herein for controlling the tag unit 115-b. In otherembodiments, the software code 425 is not directly executable by thecontroller and scheduler module 410, but it may be configured to cause acomputer, for example, when compiled and executed, to perform functionsdescribed herein.

The UWB transceiver module 450 may support radio frequency (RF)communication technology to broadcast UWB signals through the antenna(s)module 440. Likewise, the narrowband transceiver module 460 may supportRF communication technology to broadcast narrowband signals through theantenna(s) module 440. In some embodiments, the UWB transceiver module450 or the narrowband transceiver module 460, or both, include amodulator (not shown) to modulate location tracking information andprovide the modulated information to the antenna(s) module 440 fortransmission of signals. FIG. 4 shows broadcast and reception of signalsbetween the tag unit 115-b and several APs 105. In the system 400, atleast two APs 105-f and 105-g are shown communicating with the tag unit115-b; but the tag unit 115-b may communicate with more or fewer APs105.

Referring next to FIG. 5, a system 500 is illustrated with a blockdiagram. The system 500 may be configured for synchronizing APs in aposition location network in accordance with various embodiments. Insome embodiments, the system 500 includes a tracking management server150-a, which may be the tracking management server 150 of FIGS. 1Aand/or 1B. The tacking management server 150-a may include a processormodule 510, a memory module 520, a network communications module 530, asynchronized list module 540, and/or a management module 550. Themanagement module 550 may be configured to perform calibration,synchronization, coordinate determination, filter determination, channelestimation, and/or tag update mode adjustments. In some embodiments, themanagement module 550 determines or selects a master AP.

The processor module 510 may also perform various operations and mayinclude an intelligent hardware device, e.g., a CPU. In someembodiments, the processor module 510 performs various operationsassociated with synchronizing APs in a position location network. Forexample, the processor module 510 may determine what APs need to besynchronized. The tracking management server 150-a also may communicatewith a network 140-b through the network communications module 530 toreceive information from the APs 105 and/or to send information to theAPs 105. The network 140-b may be an example of the networks 140 of anyor all of FIGS. 1A, 1B, and 3.

The memory module 520 may include RAM and/or ROM. In some embodiments,the memory module 520 stores computer-readable, computer-executablesoftware code 525 containing instructions that are configured to, whenexecuted, cause the processor module 510 to perform various functionsdescribed herein. In other embodiments, the software code 525 may not bedirectly executable by the processor module 510; but the software codemodule may be configured to cause a computer, e.g., when compiled andexecuted, to perform functions described herein. The memory module 520may include a database to store a list of synchronized APs 105, and/ordetermined coordinate sets comprising coordinates of various APs 105and/or tag units 115.

The synchronized list module 540, may perform various operations and mayinclude an intelligent hardware device, e.g., a CPU. The synchronizedlist module 540 may include a database. The synchronized list module 540may store a list of synchronized APs 105. In some cases, thesynchronized list module 540 may update a stored list of synchronizedAPs 105.

FIG. 6 shows an example of a position location network 100-a inaccordance with various embodiments. The system 100-a may be an exampleof a system 100 of FIG. 1A or FIG. 1B, or both. The system 100-a may usethe communications 125 between APs 105 to synchronize the network withinthe coverage area 110. A master AP 105-h may use communications 125 todetermine which APs need to be synchronized, such as APs 105-j, 105-i,105-l, and 105-k. The APs may exchange messages 125 including oscillatorand/or timer information. In some cases, a second AP 105-l transmits anacknowledgment message to the master AP 105-h confirming thatsynchronization was successful. Upon receipt of the acknowledgmentmessage, the master AP 105-h may designate the second AP 105-l as anacting master AP.

In an embodiment, the acting master AP 105-l contains an oscillatorand/or timer(s) that are synchronized with the master AP 105-h. Theacting master AP 105-l may then be used to synchronize neighboring APs105-m and 105-n. In some cases, the acting master AP 105-l transmitsinformation relating to the APs 105-n and 105-m that have beensynchronized with the acting master AP 105-l, to the master AP 105-h. Inan embodiment, a neighboring AP 105-m may receive synchronizinginformation from more than one acting master APs 105-k and 105-l. Theneighboring AP 105-m may decide with which acting master AP—e.g., AP105-k or 105-l—to synchronize. For example, the neighboring AP 105-m maydecide which acting master AP 105-k or 105-l to synchronize with basedon the acting master AP from which it received the synchronizationinformation from first and/or the acting master AP from which thereceived synchronization information has the strongest signal strength.

Next, FIG. 7 shows a call flow diagram, which illustrates a system 700configured for synchronizing APs in a position location network within aposition location network, according to some embodiments. FIG. 7 showssynchronization between three APs 105. In the system 700, three APs105-o, 105-p, and 105-q are shown synchronizing, but synchronization mayoccur with more APs 105 as well. In some cases, a first, or master, AP105-o is used to synchronize secondary APs, such as a second AP 105-p. Afirst synchronization communication 710 between the master AP 105-o andthe second AP 105-p provides the second AP 105-p with informationnecessary to synchronize an oscillator and/or timer(s). The second AP105-p may use the information to synchronize an oscillator and/ortimer(s) 720. In some cases, the second AP 105-p transmits anacknowledgment message 730 to the master AP 105-o, to inform the masterAP 105-o that synchronization was successful.

In some cases, the master AP 105-o adds the second AP 105-p to, orupdates an existing value of, a stored synchronized list. The master AP105-o may designate 740 the second AP 105-p as an acting master AP, andAP 105-p may assist in synchronizing APs that neighbor the second AP105-p, such as a third AP 105-q. The master AP 105-o may send a message750 designating the second AP 105-p as an acting master AP. An actingmaster AP may be an AP with an oscillator and/or timer(s) that issynchronized with the master AP.

In some cases, the acting master AP 105-p broadcasts a synchronizationmessage 760 which provides the third AP 105-q with information necessaryto synchronize an oscillator and/or timer(s). The third AP 105-q may usethe information to synchronize an oscillator and/or timer(s) 770. Insome cases, the third AP 105-q transmits an acknowledgment message 780to the acting master AP 105-p, to inform the acting master AP 105-p thatsynchronization with the third AP 105-q was successful. The actingmaster AP 105-p may then send an acknowledgment message 790 to themaster AP 105-o informing the master AP 105-p that synchronization withthe third AP 105-q was successful.

In an embodiment, the third AP 105-q sends an acknowledgment messagedirectly to the master AP 105-o. In some cases, the master AP 105-o addsthe third AP 105-q to, or updates an existing value of, a storedsynchronized list. In some cases, the acting master AP 105-p maydesignate the third AP 105-q as another acting master AP. In anembodiment, the acknowledgment messages 730, 780, and 790 aretransmitted to a tracking management server. In some cases, thesynchronized list is stored and/or managed by the tracking managementserver. In still further embodiments, an acting master AP transmits alist (or an acknowledgment message representative of a list) of all APs105 which have synchronized to that acting master AP. For example, theacting master AP 105-p may transmit a list of all APs 105, which mayinclude AP105-q, that have synchronized to AP 105-p.

Those skilled in the art will recognize that the system 700 is but oneimplementation of the tools and techniques discussed herein. Theoperations of the system 700 may be rearranged or otherwise modifiedsuch that other implementations are possible.

FIG. 8 shows a flow diagram that illustrates a method 800 forsynchronizing APs in a position location network within a positionlocation network, according to various embodiments. The method 800 maybe implemented using, for example, the devices and systems 100, 200,200-a, 300, 400, 500, 100-a, and 700 of FIGS. 1A, 1B, 2A, 2B, 3, 4, 5,6, and 7.

At block 805, an AP 105, tracking management server 150, and/or someother network component may select a master AP from among a plurality ofAPs 105, each of the APs 105 having a reference oscillator and a timer.In some embodiments, the operations at block 805 are performed by themanagement module 550 of FIG. 5.

At block 810, a master AP may broadcast a first synchronization message.For example, the operations at block 810 may be performed by: the device200 of FIG. 2A; the device 200-a of FIG. 2B; the AP 105-c of FIG. 3;and/or the AP 105-h of FIG. 6.

At block 815, the master AP may receive a first acknowledgment messagefrom each AP 105 that synchronized to the master AP based on the firstsynchronization message. For example, the operations at block 815 may beperformed by: the device 200 of FIG. 2A; the acknowledgment module 230of FIG. 2B; the AP 105-c of FIG. 3; and/or the AP 105-h of FIG. 6.

At block 820, the master AP and/or the tracking management server 150,may designate as acting master APs one or more APs 105 from which anacknowledgment message is received. In some cases, the operations atblock 820 are performed by: the tracking management server 150 of FIGS.1A and/or 1B; the acting master designation module 215 of FIG. 2A; theaction master designation module 215-a of FIG. 2B; the acting masterdesignation module 215-b of FIG. 3; and/or the management module 550 ofFIG. 5.

FIG. 9 shows a flow diagram that illustrates a method 900 forsynchronizing APs in a position location network within a positionlocation network, according to some embodiments. In some cases, themethod 900 may be implemented using some or all of the devices andsystems 100, 200, 200-a, 300, 400, 500, 100-a, and 700 of FIGS. 1A, 1B,2A, 2B, 3, 4, 5, 6, and 7.

At block 905, an AP 105, tracking management server 150, and/or someother network component may select a master AP from among a plurality ofAPs 105, each of the APs 105 having a reference oscillator and a timer.In some embodiments, the operations at block 905 are performed by themanagement module 550 of FIG. 5.

At block 910, a master AP may broadcast a first synchronization message.For example, the operations at block 910 may be performed by: the device200 of FIG. 2A; the device 200-a of FIG. 2B; the AP 105-c of FIG. 3;and/or the AP 105-h of FIG. 6.

At block 915, the master AP may receive a first acknowledgment messagefrom each AP 105 that synchronized to the master AP based on the firstsynchronization message. For example, the operations at block 915 may beperformed by: the device 200 of FIG. 2A; the acknowledgment module 230of FIG. 2B; the AP 105-c of FIG. 3; and/or the AP 105-h of FIG. 6.

At block 920, the master AP and/or the tracking management server 150,may designate as acting master APs one or more APs 105 from which anacknowledgment message is received. In some cases, the operations atblock 920 are performed by: the tracking management server 150 of FIGS.1A and/or 1B; the acting master designation module 215 of FIG. 2A; theaction master designation module 215-a of FIG. 2B; the acting masterdesignation module 215-b of FIG. 3; and/or the management module 550 ofFIG. 5.

At block 925, a designated acting master AP may broadcast a secondsynchronization message. For example, the operations at block 925 may beperformed by the device 200 of FIG. 2A; the device 200-a of FIG. 2B; theAP 105-c of FIG. 3; and/or the AP 105-l of FIG. 6.

At block 930, the designated acting master AP may receive a secondacknowledgment message from each AP 105 that synchronized to thedesignated acting master AP based on the second synchronization message.In some embodiments, the operations at block 930 may be performed by thedevice 200 of FIG. 2A; the acknowledgment module 230 of FIG. 2B; the AP105-c of FIG. 3; and/or the AP 105-h of FIG. 6.

Turning to FIG. 10, which shows a flow diagram that illustrates a method1000 for synchronizing APs in a position location network within aposition location network, according to various embodiments. By way ofexample, the method 1000 is implemented using some or all of the devicesand systems 100, 200, 200-a, 300, 400, 500, 100-a, and 700 of FIGS. 1A,1B, 2A, 2B, 3, 4, 5, 6, and 7.

At block 1005, an AP 105, tracking management server 150, and/or someother network component may select a master AP from among a plurality ofAPs 105, each of the APs 105 having a reference oscillator and a timer.In some embodiments, the operations at block 1005 are performed by themanagement module 550 of FIG. 5.

At block 1010, a master AP may broadcast a first synchronizationmessage. At block 1015, the master AP may receive a first acknowledgmentmessage from each AP 105 that synchronized to the master AP based on thefirst synchronization message. For example, the operations at block 1010may be performed by: the device 200 of FIG. 2A; the device 200-a of FIG.2B; the AP 105-c of FIG. 3; and/or the AP 105-h of FIG. 6.

At block 1020, the master AP and/or the tracking management server 150,may designate as acting master APs one or more APs 105 from which anacknowledgment message is received. In some cases, the operations atblock 1020 are performed by: the tracking management server 150 of FIGS.1A and/or 1B; the acting master designation module 215 of FIG. 2A; theaction master designation module 215-a of FIG. 2B; the acting masterdesignation module 215-b of FIG. 3; and/or the management module 550 ofFIG. 5.

At block 1025, a designated acting master AP may broadcast a secondsynchronization message. For example, the operations at block 1025 maybe performed by the device 200 of FIG. 2A; the device 200-a of FIG. 2B;the AP 105-c of FIG. 3; and/or the AP 105-l of FIG. 6.

At block 1030, the designated acting master AP may receive a secondacknowledgment message from each AP 105 that synchronized to thedesignated acting master AP based on the second synchronization message.In some embodiments, the operations at block 1030 may be performed bythe device 200 of FIG. 2A; the acknowledgment module 230 of FIG. 2B; theAP 105-c of FIG. 3; and/or the AP 105-h of FIG. 6.

At block 1035, the master AP and/or the tracking management server 150may receive from the one or more designated acting master APs one ormore lists of neighboring APs 105 synchronized to the one or moredesignated acting master APs. In some cases, the operations at block1035 are performed by: the tracking management server 150 of FIGS. 1Aand/or 1B; the acting master designation module 215 of FIG. 2A; theaction master designation module 215-a of FIG. 2B; the acting masterdesignation module 215-b of FIG. 3; and/or the synchronized list module540 of FIG. 5.

It will be apparent to those skilled in the art that the methods 800,900, and 1000 are but example implementations of the tools andtechniques described herein. The methods 800, 900, and 1000 may berearranged or otherwise modified such that other implementations arepossible.

The detailed description set forth above in connection with the appendeddrawings describes exemplary embodiments and does not represent the onlyembodiments that may be implemented or that are within the scope of theclaims. The term “exemplary” used throughout this description means“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other embodiments.” The detailed descriptionincludes specific details for the purpose of providing an understandingof the described techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the described embodiments.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope and spirit of the disclosure and appended claims. For example,due to the nature of software, functions described above can beimplemented using software executed by a processor, hardware, firmware,hardwiring, or combinations of any of these. Features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C).

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not to be limited to theexamples and designs described herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of synchronizing a position location network, comprising: selecting a master access point (AP) from among a plurality of APs, each of the APs having a reference oscillator and a timer; broadcasting a first synchronization message from the master AP; receiving, at the master AP, a first acknowledgment message from each AP that synchronized to the master AP based on the first synchronization message; and designating as acting master APs one or more APs from which an acknowledgment message is received.
 2. The method of claim 1, wherein each AP is configured with a narrowband transceiver and an ultra-wideband (UWB) transceiver.
 3. The method of claim 1, wherein broadcasting the first synchronization message comprises broadcasting a narrowband signal.
 4. The method of claim 1, wherein the first synchronization message comprises information related to an oscillator frequency and a timer count.
 5. The method of claim 1, wherein an AP that synchronized to the master AP comprises an AP that estimated a frequency offset and a time offset with respect to the master AP.
 6. The method of claim 1, wherein broadcasting the first synchronization message comprises broadcasting an ultra-wideband (UWB) signal.
 7. The method of claim 1, wherein an AP that synchronized to the master AP comprises an AP that adjusted an oscillator frequency and a timer count based on the first synchronization message.
 8. The method of claim 1, further comprising: broadcasting a second synchronization message from a designated acting master AP; and receiving, at the designated acting master AP, a second acknowledgment message from each AP that synchronized to the designated acting master AP based on the second synchronization message.
 9. The method of claim 8, wherein broadcasting the second synchronization message comprises broadcasting at least one of a narrowband signal or a UWB signal.
 10. The method of claim 8, wherein the second synchronization message comprises information related to an oscillator frequency and a timer count.
 11. The method of claim 1, further comprising: receiving from the one or more designated acting master APs one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 12. The method of claim 11, wherein receiving the one or more lists comprises receiving, from the one or more designated acting master APs at the master AP, one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 13. The method of claim 11, wherein receiving the one or more lists further comprises receiving, from the master AP at a tracking management server, one or more lists of neighboring APs synchronized to at least one of the master AP and the one or more designated acting master APs.
 14. A system of synchronizing a position location network, comprising: means for selecting a master access point (AP) from among a plurality of APs, each of the APs having a reference oscillator and a timer; means for broadcasting a first synchronization message from the master AP; means for receiving, at the master AP, a first acknowledgment message from each AP that synchronized to the master AP based on the first synchronization message; and means for designating as acting master APs one or more APs from which an acknowledgment message is received.
 15. The system of claim 14, wherein each AP is configured with a narrowband transceiver and an ultra-wideband (UWB) transceiver.
 16. The system of claim 14, wherein broadcasting the first synchronization message comprises broadcasting a narrowband signal.
 17. The system of claim 14, wherein the first synchronization message comprises information related to an oscillator frequency and a timer count.
 18. The system of claim 14, wherein an AP that synchronized to the master AP comprises an AP that estimated a frequency offset and a time offset with respect to the master AP.
 19. The system of claim 14, wherein broadcasting the first synchronization message comprises broadcasting an ultra-wideband (UWB) signal.
 20. The system of claim 14, wherein an AP that synchronized to the master AP comprises an AP that adjusted an oscillator frequency and a timer count based on the first synchronization message.
 21. The system of claim 14, further comprising: means for broadcasting a second synchronization message from a designated acting master AP; and means for receiving, at the designated acting master AP, a second acknowledgment message from each AP that synchronized to the designated acting master AP based on the second synchronization message.
 22. The system of claim 21, wherein broadcasting the second synchronization message comprises broadcasting at least one of a narrowband signal or an UWB signal.
 23. The system of claim 21, wherein the second synchronization message comprises information related to an oscillator frequency and a timer count.
 24. The system of claim 14, further comprising: means for receiving from the one or more designated acting master APs one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 25. The system of claim 24, wherein receiving the one or more lists comprises receiving, from the one or more designated acting master APs at the master AP, one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 26. The system of claim 24, wherein receiving the one or more lists further comprises receiving, from the master AP at a tracking management server, one or more lists of neighboring APs synchronized to at least one of the master AP and the one or more designated acting master APs.
 27. An apparatus for synchronizing a position location network, comprising: a processor; memory in electronic communication with the processor; and instructions stored in the memory, the instructions being executable by the processor to: broadcast a first synchronization message from the master AP; receive, at the master AP, a first acknowledgment message from each AP that synchronized to the master AP based on the first synchronization message; and designate as acting master APs one or more APs from which an acknowledgment message is received.
 28. The apparatus of claim 27, wherein the instructions executable by the processor to broadcast the first synchronization message comprise instructions executable by the processor to broadcast a narrowband signal.
 29. The apparatus of claim 27, wherein the first synchronization message comprises information related to an oscillator frequency and a timer count.
 30. The apparatus of claim 27, wherein an AP that synchronized to the master AP comprises an AP that estimated a frequency offset and a time offset with respect to the master AP.
 31. The apparatus of claim 27, wherein the instructions executable by the processor to broadcast the first synchronization message comprise instructions executable by the processor to broadcast an ultra-wideband (UWB) signal.
 32. The apparatus of claim 27, wherein an AP that synchronized to the master AP comprises an AP that adjusted an oscillator frequency and a timer count based on the first synchronization message.
 33. The apparatus of claim 27, wherein the instructions are further executable by the processor to: broadcast a second synchronization message from a designated acting master AP; and receive, at the designated acting master AP, a second acknowledgment message from each AP that synchronized to the designated acting master AP based on the second synchronization message.
 34. The apparatus of claim 33, wherein the instructions executable by the processor to broadcast the second message comprise instructions executable by the processor to broadcast at least one of a narrowband or a UWB signal.
 35. The apparatus of claim 33, wherein the second synchronization message comprises information related to an oscillator frequency and a timer count.
 36. The apparatus of claim 27, wherein the instructions are further executable by the processor to: receive from the one or more designated acting master APs one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 37. The apparatus of claim 36, wherein the instructions executable by the processor to receive the one or more lists comprise instructions executable by the processor to receive, from the one or more designated acting master APs at that master AP, one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 38. The apparatus of claim 36, wherein the instructions executable by the processor to receive the one or more lists comprise instructions executable by the processor to receive, from the master AP at a tracking management server, one or more lists of neighboring APs synchronized to at least one of the master AP and the one or more designated acting master APs.
 39. A computer-program product for synchronizing a position location network, the computer-program product comprising a non-transitory computer-readable medium storing instructions executable by a processor to: broadcast a first synchronization message from the master AP; receive, at the master AP, a first acknowledgment message from each AP that synchronized to the master AP based on the first synchronization message; and designate as acting master APs one or more APs from which an acknowledgment message is received.
 40. The computer-program product of claim 39, wherein the instructions executable by the processor to broadcast the first synchronization message comprise instructions executable by the processor to broadcast a narrowband signal.
 41. The computer-program product of claim 39, wherein the first synchronization message comprises information related to an oscillator frequency and a timer count.
 42. The computer-program product of claim 39, wherein an AP that synchronized to the master AP comprises an AP that estimated a frequency offset and a time offset with respect to the master AP.
 43. The computer-program product of claim 39, wherein the instructions executable by the processor to broadcast the first synchronization message comprise instructions executable by the processor to broadcast an ultra-wideband (UWB) signal.
 44. The computer-program product of claim 39, wherein an AP that synchronized to the master AP comprises an AP that adjusted an oscillator frequency and a timer count based on the first synchronization message.
 45. The computer-program product of claim 39, wherein the instructions are further executable by the processor to: broadcast a second synchronization message from a designated acting master AP; and receive, at the designated acting master AP, a second acknowledgment message from each AP that synchronized to the designated acting master AP based on the second synchronization message.
 46. The computer-program product of claim 45, wherein the instructions executable by the processor to broadcast the second message comprise instructions executable by the processor to broadcast at least one of a narrowband or a UWB signal.
 47. The computer-program product of claim 45, wherein the second synchronization message comprises information related to an oscillator frequency and a timer count.
 48. The computer-program product of claim 39, wherein the instructions are further executable by the processor to: receive from the one or more designated acting master APs one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 49. The computer-program product of claim 48, wherein the instructions executable by the processor to receive the one or more lists comprise instructions executable by the processor to receive, from the one or more designated acting master APs at that master AP, one or more lists of neighboring APs synchronized to the one or more designated acting master APs.
 50. The computer-program product of claim 48, wherein the instructions executable by the processor to receive the one or more lists comprise instructions executable by the processor to receive, from the master AP at a tracking management server, one or more lists of neighboring APs synchronized to at least one of the master AP and the one or more designated acting master APs. 